In conventional Long Term Evolution (LTE for short) communications technologies, signaling and data exchange between user terminals (full name: user equipment, UE for short) needs to pass through an evolved NodeB (eNB for short or base station) to which each terminal belongs.
In user direct-connection communication (that is, device to device, D2D for short) that is used as a direct communications technology, data exchange between UEs does not need to be forwarded by using an eNB, the exchange can be directly performed between the UEs, or the exchange is directly performed under the assistance of a network.
However, synchronization signals transmitted by UEs that perform user direct-connection communication affect each other, causing poor quality of communication or even a communication failure.